Identity theft is a huge problem with the IRS.
Identity Protection: Prevention, Detection and Victim Assistance
Read this:
1.File a report with the local police.
2.File a complaint with the Federal Trade Commission at
www.identitytheft.gov or the FTC Identity Theft Hotline at 1-877-438-4338 or TTY 1-866-653-4261.
http://www.irs.gov/pub/irs-pdf/p5027.pdf
....and if you were a client of mine I would advise you to file form 14039 (Identity theft Affidavit).
ASAP See Sec.A Q-2.
Otherwise, someone else will probably file using your SSN as soon as they open the e-file window next year, and you will have to file it then.
http://www.irs.gov/pub/irs-pdf/f14039.pdf
I wish you good luck. You're gonna need it.
Click on the link to see current steps being taken. I read about this "Security Summit" the other day.